Adaptive 2 Flashcards
(38 cards)
What is cell mediated immunity?
Antigen-receptor effector T cells dominate
T help CD4 and cytotoxic CD8
Responsible for chronic inflammation, tumor immunity and graft rejection
What are the subtypes of CD4 helper T cells?
TH1 activate macrophages
TH2 activate B cells
Tregs: suppressor aberrant pathological immune responses
TH17: assist B cells to make antibodies, activate macrophages, recruit immune cells (loss linked to chronic inflammation)
What are the subtypes of CD8 cytotoxic T cells?
TH17 cells: create inflammation and tissue injury in autoimmune disease
T regulatory cells (Tregs): shut down immune responses after they have successfully eliminated invading organisms and prevent autoimmunity
How do T cells differ form B cells?
TCR bind antigen but not native antigen (unlike antibodies)
TCR binds antigens already broken down and present on surface of APC
Cell to cell contact is always required between T cell and APC
T cells never secrete their antigen specific receptor
Describe antigen presentation to T cells. How are antigen presented?
T cells do not recognize intact antigens
T cells recognize antigens that have been digested into peptides and combined with MHC
MHC bring peptides to cell surface and display do they can be recognized by T cells
MHC proteins plus antigen fragments= antigen presentation
What are MHCs (human leukocyte antigen)?
Dimeric surface glycoproteins that control adaptive immune response (on chromosome 6)
Present antigens to T cells to distinguish self and non self
Each has one binding site, no capacity to rearrange or structurally change (similar to immunoglobulin)
In the transplantation process what is MHC used for?
Tissue typing, determination of HLA genotypes of donor and recipient (only identical twins have same MHC 1)
Describe the differences between MHC 1 and MHC 2. What are they regulated by?
MHC 1: Present on the surface of all nucleated cells (so
excludes mature RBCs), samples the internal contents of a cell and displays peptides to the immune system.
MHC 2: Present only on APCs, Associates with peptides from within vesicles (i.e. acquired outside the cell), nonidentical polypeptide chain
Expression regulated by cytokines
What are MHC 1 and 2 each recognized by?
MHC 1: CD8
MHC 2: CD4
Describe APCs, Examples?
Internalize and degrade antigens into 10-30 amino acids for loading onto MHC 1 and 2
Ex: dendritic cells, macrophages, langerhans cells, B cells
What are considered the professional APCs?
Dendritic cells are most efficient
Found in tissues in contact with external environment
Only cells that present antigen to naive T cells
What MHC complex forms on vaccinated cells?
MHC 1
Spike proteins form spikes that migrate to cell surface
Vaccinated cells also break up some of the proteins and present them
MHC plus spike binds on cell surface
What kind of MHC complex forms on dead vaccinated cells?
MHC 2
Debris from dead cell contains spike proteins can be taken up by APC
Describe T cell Receptors, What do they bind, what is the most abundant, what are they made out of?
Bind to MHC peptide complexes
Most abundant is a disulfide-linked heterodimer transmembrane complex of alpha and beta chains
Constant and variable region, constant region anchored in cell membrane
Do T cell receptors go through somatic mutations?
No
What region of the T cell receptors recognize antigens? How do they diversify? Where does this occur?
Variable
diversity in T cells receptors is generated during gene rearrangement focused on CDR 3 regions (hyper variable)
Occurs in the thymus
For a T cell to be functional what does it need?
TCR that can recognize antigen with MHC
Expression of CD4 or CD8 coreceptor
TCR must be linked to another cell surface molecule
When are CD4 and CD 8 cells expressed?
Once cells reach the thymus
Describe the process of thymic education that TCR undergo.
Eliminates self reactive T cells and require that T cells recognize either MHC 1 or 2
Epithelial cells in Cortex mediate positive selection
Dendritic cells in medulla mediate negative selection
Describe the positive and negative selection that occurs during T cell development.
TCR must recognize MHC and pathogen peptides
Positive selection: T cells with low affinity for self MHC survive, decides if T cell becomes CD 4 or CD8
Negative selection: deletes T cells that have high affinity for self peptides and self MHC
What CD cells are MH 1 and 2 accociated with?
T cells that recognize MHC 1 receive a survival
signal for CD8 and stop expressing CD4.
T cells that recognize MHC 2 receive a survival
signal for CD4 and stop expressing CD8
What happens to mature naive T cells that are self MHC-restricted and tolerant to many self antigens?
Leave the thymus and populate lymph nodes, spleen and MALT
Describe the process by which T cell are activated and lymphokines are released.
T-cells recognize antigen in the context of an MHC molecule on the cell surface.
The 3 hypervariable regions (CDRs) in the variable domain recognize antigen.
Upon recognition of a specific antigen, the signal is passed to CD3 (required for T cell activation), which relays the signal, prompting T-cell activation and the release of lymphokines.
Compare B and T cells.
Effector B cells secrete antibodies; heavy chain constant (C)
region isotypes trigger distinct effector mechanisms.
Effector T cell functions depend on cell to cell contact and are not mediated directly by the T cell receptor, which serves only for antigen recognition.
THERE IS NO CLASS SWITCHING IN T CELLS!
